Due to the increasing speed of wireless and wired communications, the offers for contents to be downloaded on a terminal of an end user, for example a personal computer, a PDA (personal digital assistant) or a mobile phone etc., have highly increased. These contents can be for example pictures, melodies, songs, games, all kind of software or other data and the like. With the increasing offer of such contents, there also arises the demand for a reliable charging system that can handle various types of services and different charging methods. In general, a service can be a call between end users, a communication session between an end user and a server to download or upload content, or any other interaction between a terminal and a third party.
For the purpose of the present invention to be described herein below, it should be noted that                a terminal may for example be any kind of communication device, such as wireless or wired devices, e.g. personal computers, mobile phones or the like, irrespective of a specific standard to which these conform as long as they are compatible with the charging system;        for the charging system any suitable protocol for operating/message exchange is possible; only as an example it is noted that Diameter as a follow-up of RADIUS (Remote Authentication Dial-In User Service) is particularly suitable to be used with the present invention;        method steps likely to be implemented as software code portions and being run using a processor at one of the server/client entities, are software code independent and can be specified using any known or future developed programming language as long as the functionality defined by the method steps is preserved;        generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the present invention in terms of the functionality implemented;        method steps and/or devices likely to be implemented as hardware components at one of the server/client entities are hardware independent and can be implemented using any known or future developed hardware technology or any hybrids of these, such as MOS, CMOS, BiCMOS, ECL, TTL, etc., using for example ASIC components or DSP components, as an example;        devices can be implemented as individual devices, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device is preserved.        
As a specific example only, reference is made to document RFC4006 which specifies a protocol for Diameter application that can be used to implement credit-control for a variety of end user services such as network access, Session Initiation Protocol (SIP) services, messaging services, and download services. Upon request of an end user, a client transmits a service request to a server. The server responds to the request by sending an answer, thereby reserving quota for the requested service from the end user's account. Then the client allows service delivery to the end user and starts monitoring the usage of the granted quota. When the quota granted to the user has expired or the service has been successfully delivered or terminated, the client sends a message to the server reporting the used amount. Then, the server deducts the used amount from the end user's account.
However, a problem arises if the service requested by the end user is of a predetermined type such as free-of-charge. In this case, the server will not reserve any quota for the requested service, but will issue an answer including a code indicating that credit-control is not applicable for the requested service. In this instance, the client will not report to the charging system anymore and if there is possibility that the service can change from free-of-charge to chargeable, there could probably be credit loss for an operator.
In order to avoid such situation, the server would need to issue a request for re-authorization to the client. This would mean that, for each session, the server would need to keep track of the possibility that the service can change from free-of-charge to chargeable. However, this would impose a large processing and monitoring burden on the server.
Also in cases in which the server grants a requested service without reserving any quota, the charging method is not indicated and usage of service, if reported, can not be allocated to a specific charging method.